The powerhead of a boat or any other watercraft can be placed either inside (inboard) or outside (outboard) the hull of the boat. In both cases, a water jet apparatus can be mounted outside the boat at a certain depth below the waterline.
For example, it is well-known to retrofit a water jet on an outboard motor in place of a propeller. In such a system, a rotor or impeller is mounted (e.g., spline fitted) directly on the propeller output shaft in place of the propeller. There are typically no modifications to the drive train, cooling or sealing components. A housing having a water inlet and a water outlet surrounds the rotor.
A water jet system has the advantages of protecting the rotating elements from interference with and damage by foreign objects in the water, and improving some aspects of performance of the propulsion system. Another benefit inherent with the water jet is a directed jet of water that results in greater steering response at speed.
To facilitate use of water jet-propelled boats in shallow water, it is known to mount the water jet at an elevation such that the water jet does not project below the bottom of the boat hull. This can be accomplished, for example, by installing a duct in the stern of the boat, the duct being arranged to connect one or more inlet holes formed in the bottom of the hull with an outlet hole formed in the transom. The water jet is then installed outside the hull in a position such that the water jet inlet is in flow communication with the duct outlet at the transom.
Alternatively, some water jets are designed with an inlet housing which is built into the hull such that the inlet lies in the plane of the hull bottom. In a typical design, an inlet housing which rotatably supports a first shaft is mounted to the boat hull, and then a stator housing which rotatably supports a second shaft is attached to the inlet housing. The impeller is securely mounted on the forward end of the second shaft and has a splined bore for receiving a splined end of the first shaft when the inlet and stator housing are coupled. This conventional arrangement requires two sets of bearings: one set installed in the inlet housing for rotatably supporting the first shaft at two axial positions therealong and another set installed in the stator housing for rotatably supporting the second shaft at two axial positions therealong.
There is a need for a water jet apparatus having a simplified design which is relatively easier to mount onto a boat hull.